1. Field of the Invention
This invention relates generally to liquid level monitors, and more particularly to improvements in the monitoring apparati disclosed and claimed in U.S. Pat. Nos. 4,840,137 and 4,859,987. The first of these patents issued Jun. 20, 1989, is entitled LIQUID LEVEL GAUGING APPARATUS, and has common ownership with the present application. U.S. Pat. No. 4,859,987 issued Aug. 22, 1989, is entitled APPARATUS AND METHOD FOR MONITORING LIQUID LEVELS and also has common ownership with the present application. Accordingly, the entire disclosures of U.S. Pat. Nos. 4,840,137 and 4,859,987 are specifically incorporated by reference, into the present application.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
In U.S. Pat. No. 4,840,137 above identified, the disclosed monitor employs a photocell and light emitting diode housed in a cup-like prism which has at its outer end a generally conical surface indicated by the reference numeral 102. This device was intended to be installed in the wall of the oil pan of an automotive vehicle. Its operation, as indicated in column 12, lines 31-36, is as follows: When the oil level in the pan is below a certain point on the cone 102, light from the light emitting diode is reflected internally of the cone and impinges upon the phototransistor, causing it to conduct. The resultant condition is employed to drive circuitry that provides the desired warning, namely to the effect that a low oil level exists in the pan.
However, when the oil level is normal, the cone 102 is covered and light impinging on the oil-cone interface is not sufficient, following reflection within the prism, to trigger the phototransistor.
While the disclosed arrangement has successfully been in use commercially for several years, attempts were made to extend the application of the apparatus to other equipment involving monitoring the level of various other liquids of the automobile.
The present invention constitutes an improvement by which the level of liquids other than crankcase oil can be monitored, as for example the coolant in the radiator of an automobile engine, heat exchanger, or other equipment.
An effort was made to adapt the monitor device of U.S. Pat. No. 4,840,137 for use with an automobile radiator. However, it was found that special conditions existed in radiators due to the heat exchanger core being closely jacketed at the reservoir area, which resulted in extremely confined spaces whereby under conditions of normal liquid levels and with liquids of a type which are generally more translucent than motor oil, substantial undesirable amounts of light were passing out through the surface of the cone 102, through the radiator liquid, striking a closely-located opposite internal surface of the radiator at the reservoir area, and then being reflected back to the cone in a manner to register on the phototransistor as an erroneous low level indication.
The reflective surface of the reservoir area in this case was within a fraction of an inch of the cone, typically less than one-quarter of an inch.